Litter bugs can save world from running out of chocolate

They may be too small, but according to a recent study, the litter bugs can help protect the world's chocolate supply.

Scientists at the Smithsonian Tropical Research Institute (STRI) in Panama found that exposing baby cacao plants to microbes from healthy adult cacao plants reduced the plant's chance of becoming infected with the serious cacao pathogen, Phytopthora palmivora, by half.

"When human babies pass through the birth canal, their bodies pick up a suite of bacteria and fungi from their mother. These microbes strengthen their immune system and make the baby healthier," said lead author Natalie Christian from the University of Indiana. "We showed that an analogous process happens in plants: adult cacao trees also pass along protective microbes to baby cacao plants."

Researchers at STRI have investigated the interactions between plants and their microbes for the past 20 years. They were the first to show that in tropical forests, where cacao grows, every leaf is home to hundreds of different fungi and bacteria, and that applying helpful microbes to leaves in field treatments protected cacao from disease.

Researchers found that specific fungal species, such as Colletotrichum tropicale, protect plants from their enemies--the pathogens and insects that eat them. Research at STRI has also shown that, as with humans, microbes stimulate plants' ability to defend themselves and has demonstrated the magnitude and extent of endophyte effects on host genetic expression.

"We discovered both by culturing the microbes from the leaves and also by directly sequencing fungal DNA from plant tissue, that one of the most common fungi on the cacao seedlings was their protector, Colletotricum tropicale. And not only that, but it was also much more common on the leaves of young plants grown with leaf litter from healthy cacao adults," said Christian. "What this means is that C. tropicale from leaf litter from adult trees is able to quickly get into young leaves and crowd out other microbes, including pathogens, thus keeping them from colonizing."

"Not only did this show us that starting seedlings out surrounded by leaves from healthy adults may vastly improve their health -- a result potentially very important to the cacao industry -- for the first time, we are beginning to understand how microbial communities assemble on leaves of cacao and other species in nature and what may influence their ability to protect plants," said co-author Allen Herre.